Methods of making contamintant-proof electrical circuit components



L. E. RAVlCH 3,052,012

METHODS OF MAKING CONTAMINANT-PROOF ELECTRICAL CIRCUIT COMPONENTS Sept.4, 1962 2 Sheets-Sheet 1 Original Filed Feb. 5, 1953 INVENTOR ATTORNEYSSept. 4, 1962 E. RAVICH 3,052,012

METHODS OF MAKING CONTAMINANT-PROOF ELECTRICAL CIRCUIT COMPONENTSOriginal Filed Feb. 5, 1953 2 Sheets-Sheet 2 INVENTOR LEONARD E. RAVICHATTORNEYS Unite This invention relates to improvements in electricalcircuit components and more particularly to improvements in theprotection of such components from. extraneous influences such asatmosphere conditions or substances which would modify the electricalcharacteristics of such components.

This application is a division of my co-pending application Serial No.335,381 filed February 5, 1953, now Patent No. 2,833,942..

In the use of many delicate electrical circuit components such ascrystalline structures, printed circuits, and the like it is necessaryto maintain such components as free as possible of any contaminantswhich might settle or collect on the component and affect its accuracyof operation by changing its normal operating characteristics. I haveinvented an improved structure for protecting such components fromcontamination and the method of making such structures, which I willdescribe by way of example in connection with frequency control crystalsfor electronic devices. While such crystals are in fact accurately cutcrystal fragments, they will be referred to herein as crystals in viewof the general use of that term for that purpose in the industry. Thestructure and method herein described is, however, equally applicable toprinted circuits, transistors, photo-transistors, thermal responsivetransistors, crystalline rectifiers and other electrical circuitcomponents the operating characteristics of which could be modified byan accumulation of extraneous material thereon, in handling duringmanufacturing, assembly, shipping, or operating procedures, or byatmospheric conditions such as temperature and humidity.

Frequency control crystals as used in radio and electronic devicesusually comprise a quartz crystal fragment operatively connected bysilver contact points, provided thereon, to a pair of spaced electrodes,such that the crystal is held in a suspended relation between theelectrodes. The electrodes may in turn be secured, as by soldering, to apair of hollow pins or mounting legs which are rigidly secured in aglass, porcelain or other insulating base and which, when the unit isplugged into a complementary socket, form a support for the crystal unitas well as electrical connections to the crystal. A metallic protectivecover or can encircles the suspended quartz crystal and in past practiceis secured in airtight relation to the base to form an airtight chamberfor the suspended crystals. In prior art devices the can was evacuatedthrough a suitable aperture provided therein, filled with an inert gassuch as nitrogen, and then sealed thus forming an inert atmosphereenveloping the crystal.

After the inert atmosphere has been created in the container or can thecrystal is given a final test for its frequency characteristics toascertain whether such characteristics have been modified by itsmounting within the container.

It is essential in such devices that the operating characteristics ofthe crystal remain the same such that there will be no variation in thefrequency characteristics under widely divergent operating conditions,as might be encountered for example in installations of militaryequipment that may be used in either the polar regions or tropics.Experience has shown that the deposit of even 3,5Z,lll2 Patented Sept.4, 1962 minute amounts of a foreign substance on a crystal or slightvariations in atmospheric conditions materially affects the frequencycharacteristics of the crystal during its operation. For this reason,military specifications are particularly rigid in its requirements ofoperation of such apparatus.

The structure and assembling techniques heretofore known in the art havenot been wholly satisfactory and, even though minute, such foreignsubstances as grease, oil, soldering flux residue, inorganic or organicsalts and other contaminants frequently have been deposited on thequartz crystals during assembly handling or the crystal has beeneffected by temperature or humidity. Additionally, if any of theaforementioned contaminants are present within the container thevibration of the crystal and the heat subsequently produced will cause amigration of the foreign matter onto the crystal surface thus changingits frequency output.

By the very nature of prior art devices such contaminated conditions arenot determinable any earlier than final test of the unit after the coverhas been placed over the crystal and secured to the base, and oftentimessuch conditions do not manifest themselves until the units have beeninstalled in the field. Consequently, there have heretofore been arestrictively high number of units rejected in final test because theydo not meet the rigid specifications, and a commensurately high numberof units have been discarded in the field because they manifested, atsuch later time, a contaminated condition. As a result, manufacturingcosts have been exorbitantly high and the number of satisfactory unitsproduced has heretofore been extremely low.

The present invention contemplates a novel shield for electrical circuitcomponents and the method of producing such shield which will give acompletely satisfactory unit and which will permit the final testing ofthe circuit component before the final or complete assembly of the unitsfor field use.

This novel structure contemplates the enveloping of the circuitcomponent in a small hollow shield or bubble structure that is thenevacuated or filled with an inert gas to provide an inert atmosphere.The metallic cover which heretofore served the dual purpose of aprotective cover and a means for maintaining an evacuated or inertatmosphere around the circuit components serves only as a cover in mynovel structure. As a result, the crystals can be fully tested beforesecuring them to a mounting base or before the covers are ever assembledthereon. This feature reduces the hazards of contaminants on the cover,on the hands of the assembler, or in the materials used to assemble thecovers from ever contacting the crystals, thereby assuring a greaterquantity of crystals capable of meeting the rigid operationalspecifications, materially reduces the cost of producing such crystals,and lessens the number of operations necessary before final testing ofthe crystals is possible.

It is therefore a major object of this invention to provide an improvedstructure for protecting contaminant sensitive circuit components fromsources of contarnination;

Another object of this invention is to provide an improved shield forencasing and protecting contaminant sensitive circuit components in acontaminant free atmosphere and methods of producing such shield;

A further object of this invention is to provide a contaminant sensitivecircuit component, such as a crystal, which is supported betweendelicate spaced electrodes with a protective airtight hollow plasticshield or bubble for protecting the crystal from contaminants and toprovide methods of forming such a plastic shield;

And another object of this invention is to provide a novel hollow shieldor bubble for suspending electronic crystals therein and novel means forcreating an inert atmosphere within the bubble.

These and other objects will appear from the following description andappended claims when read in connection with the attached drawing,wherein;

FIGURE 1 is an enlarged perspective view of a standard disc-shapedcrystal showing one of the silver contacts for the mounting of theelectrodes;

FIGURE 2 is a top plan view of a standard rectangular shaped crystalshowing in enlarged form silver contact strips for mounting of theelectrodes;

FIGURE 3 is an enlarged perspective View partially in section showing arectangular crystal with electrodes secured to a mounting base;

FIGURE 4 is an enlarged perspective view showing a disc crystal withelectrodes secured to a mounting base;

FIGURE 5 is a front elevational view of the crystal shown in FIGURE 2;

FIGURE 6 is an enlarged perspective view of two halves of one form ofshield or bubble;

FIGURE 7 is a perspective view of the metallic cover;

FIGURE 8 is an enlarged perspective view showing a disc shaped crystalencased by a shield or bubble and showing an evacuating needle extendinginto the bubble;

FIGURE 9 is 'a side elevational view of a rectangular shaped crystalencased in a modified form of shield or bubble;

FIGURE 10 is a front perspective view of a completely assembled unitillustrating the cover and showing the shield encased crystal in phantomlines;

FIGURE 11 is a three-quarter perspective view of the assembly shown inFIGURE 10;

FIGURE 12 is a sectional view taken substantially along the line 1212 ofFIGURE 10;

FIGURE 13 is a front elevational view of a disc type crystal showing amodified silver contact, modified means of securing the electrodes tothe contacts, and a modified protective cocoon;

FIGURE 14 is a top plan view of the crystal shown in FIGURE 13 showingthe oval shape of the modified cocoon;

FIGURE 15 is a front elevational view of a rectangular type crystalshowing similar contacts and electrode securing means as shown in FIGURE13 and further showing a rectangularly shaped protective cocoon;

FIGURE 16 is a top plan view of the crystal shown in FIGURE 15 showingthe rectangular shape of the cocoon;

FIGURE 17 is a vertical sectional view of exemplary apparatus used inthe method of assembling the protective cocoons in an inert atmosphere;and

FIGURE 18 is a perspective view showing the mass strip production of theform of protective cocoon shown in FIGURE 9.

Referring now to FIGURES 1 and 2 there is shown two types of standardfrequency control quartz crystals widely used in electronic devices.Numeral 20 indicates a disc type crystal and 22 indicates a standardrectangular shaped crystal. As is clearly seen in FIGURE 1, disc 20 isprovided with an electrode mounting point 24 of silver solder A similarcontact point is mounted on the opposite side of the disc spaced fromcontact point 24 by the intervening quartz crystal '20. In thecrystalline structure shown in FIGURES 2 and 5 the silver contact pointscomprise silver solder strips 26 and 28 disposed on opposite sides ofcrystal body 22. The silver contact points or strips, which may beapplied to either crystal body 20 or 22 by an evaporation process, whileserving as a mounting point add weight to the crystals to modify itsfrequency characteristics. In the case of disc type crystal 20, asclearly seen in FIGURE 4, electrodes 30 and 32 are respectively securedto the silver contacts on opposite sides at the exact center of the discby suitable means, such as soldering. Electrodes 30 and 32 extendperpendicularly outwardly from their respective faces a short distanceand are then bent at right angles to have vertically downward- 4 1yextending legs 34 and 36, respectively. As clearly seen in FIGURE 3electrodes 38 and 40 are similarly secured to silver strips 26 and 28 atthe exact center of side faces 42 and 44 and extend perpendicularlyoutwardly therefrom and then are bent into vertically downwardlydisposed legs 46 and 48.

In the case of either the disc or rectangular type of crystal themounting structure for the crystal preferably comprises a base 50 ofporcelain, glass, or other suitable material, in which there is provideda pair of spaced apertures for rigidly mounting, by suitable means, apair of hollow mounting contact pins or prongs 52 and 54. Electrode legs46 and 48 are inserted into hollow pins 52 and 54, respectively, andrigidly securedtherein as by soldering.

The foregoing has been the known and conventional method of assemblingsuch crystals. At this point in prior art devices a metallic cover 56,such as is shown in FIG- URE 7 was secured to base 50 and evacuatedthrough aperture 58 to form an inert atmosphere around the crystal. Asheretofore noted such structure and methods of assembly exposed thecrystal to the deposit of foreign substances, which it is the purpose ofthe present invention to obviate, both prior to and during theattachment of and modification of the atmosphere within the cover 56.

Referring to FIGURE 6 there is shown two exactly similar hemispheres 60and 62 formed of a suitable electrical insulating material such as aninsulating plastic however it is to be noted that any desired shapes maybe employed. Hemispheres 60 and 62 are brought together along theircircular bases with the crystal in non-contacting relation with thehemispheres therebetween and with electrode legs 36 and 34 or 46 and 48extending externally intermediate the two hemispheres to form a unitarycocoon or bubble 64, as clearly seen in FIGURES 8, 10 and 11. The edgesof the two hemispheres are fixed together in sealed relation by suitablemeans such as direct or inductive heat, by pressure adhesives, or by anysuitable means. The sealing together of the hemispheres rigidlysurrounds and secures the electrode legs therebetween as is clearly seenin FIGURES 8, 9 and 12. By this construction, the circuit component issuspended within the hollow space formed by the joined hemispheres.After hemispheres 60 and 62 are sealed together in fluid tight relation,a heated hollow needle 66 may be inserted through a side of the cocoonor bubble into the chamber joined by the hemispheres to permitevacuation of the chamber and/or for the filling of the chamber with aninert gas, such as nitrogen. The needle is maintained hot so that as itis withdrawn the bubble in the vicinity of the needle is in a plasticcondition and will immediately seal the opening made by the needle, thuscompletely sealing the crystal in a controlled atmosphere within theshield or bubble.

Since the hemispheres are kept completely clean and, since no fluxes orsolders are used to join them, or to seal the opening through which thechamber is evacuated the possibility of foreign deposits contacting thecircuit component are immensely minimized.

As heretofore noted the hemispheres are preferably formed of plasticinsulating material which contains no volatile matter. By containing novolatile matter, I mean a material which is not volatile at temperaturesand conditions which will be experienced during intended operation. Amaterial which I have found to be ideally suited is a plasticcomposition known as Mylar and manufactured by the Dupont ChemicalCompany. Chemically this material is polyethylene glycol terephthalateand is available in sheets varying in thickness from A mil to 7 mils,and is easily formed into the desired hemispheres by well-known moldingmethods. This material is completely flexible at temperatures varyingfrom 60 degrees centigrade to plus degrees centigrade and has anextremely low vapor pressure making it ideally suited for installationsthat may have use in either polar or tropic regions. As a result whenthis material is formed into a protective hollow shield for the circuitcomponent, neither the evacuation procedure of the cocoon nor the slightamount of heat which may be present in the component unit will cause anycontamination of the crystal from materials in the plastic such asplasticizers. This is extremely important since it is essential toperfect operation, as heretofore noted, that the components such ascrystals be kept clean or uncontaminated.

After the shield or bubble, formed by hemispheres 61B and 62, has beensealed the crystal can be finally tested for its frequencycharacteristics. The structure of this novel invention by-passes thenecessity of securing the electrodes to base 50 or securing covering 56to base 56 and the necessary soldering steps which heretofore werenecessary to test the crystal and which exposed the crystal to theforeign substances involved in this operation, thereby multiplying thechances of contaminating the crystal.

Once the crystal or electrical circuit component has passed or met thetest requirements, protective cover 56 is placed over the shieldedcrystal unit, as clearly seen in FIGURES l0 and 11, to fit closelyaround the periphery of base 50 to which it is secured, by suitablemeans. It is unnecessary of course with my novel invention to have anairtight seal between base 50 and cover 56 since the cover is not neededto maintain an inert atmosphere around the electrical circuit component,but merely forms a protective covering.

Referring to FIGURE 12 there is shown a sectional view takensubstantially along the line 1212 of FIG- URE 10. As clearly seen inthis figure the sealing of the two hemispheres 60 and 62 along partingline 68 causes the edges of the two hemispheres to firmly and sealinglyengage the electrode legs 46 and 48 (or 34 and 36) therebetween to forma support to hold the bubble or shield 64 in spaced relation to thecrystal or electrical component suspended therein.

Turning now to FIGURE 9 there is shown a modified form of shield orbubble comprising a pair of rectangular sheet 70 and 72 of plastic orother suitable material. Hemispheres or bubbles 74 and 76 are moldedinto the center of sheets 71} and 72, respectively, as clearly seen inFIGURE 9, with a planar surface of the sheets surrounding the bubbles.Like hemispheres 60 and 62, sheets 70 and '72 are brought together andsealed along their flat faces, as indicated by parting line 78 to forman airtight chamber about crystal 22. The electrode legs 46 and 48 (or34 and 36) extend through the planar portion of the sheets and protrudefrom an edge 86 thereof to permit mounting in pins 52 and 54. In thisform of shield or bubble, the edge 84} of the joined sheets may rest onthe upper surface of base 50 and the portion of the electrodes betweenthe upper surface 50 and the shield are completely enveloped betweensheets 70 and 72 thus affording better support and protection for thedelicate electrodes. Additionally this form of shield affords excellentadaptability to mass production techniques since long sheets havingthese depressed portions or spaced bubbles can be produced, as isclearly seen in FIGURE 18. As seen in FIGURE 18 sheets 70 and 72 arelong continuous strips having spaced bubbles 74 and 76 respectively. Anelectrical circuit component unit such as a crystal provided withelectrodes and with or without a mounting base is positioned betweeneach opposed pair of concavities as indicated generally at 82 and faces84 and 86 are brought together and sealed. After sheets 70 and 72 aresealed together the sheets are cut along lines 88 to separate the sealedunits to permit further operations upon the individual assemblies.

Referring now to FIGURES 13 through 15 there is shown furthermodifications of crystal with modified contact points, modifiedelectrode securing means, and a further embodiment of the protectivecocoon or shield.

As clearly seen in FIGURE 13 disc crystal 90 is provided with silvercontact strips 92 and 94 on opposite sides of the disc and extendingtoward the center of the disc where they terminate in circular portions96 and 98, respectively. These strips are preferably formed on the discby means of the aforementioned evaporation process. Electrodes 100 and102 are each formed at one end with double loops 104 and 106 and 198 and110, respectively as best seen in FIGURE 14. Crystal 911 is insertedbetween these loops with the loops gripping the crystal and a respectivesilver contact point, much like the manner of a paper clip. A smallportion of silver solder secures one of the loops of each electrode toits associated silver contact strip to positively secure the electrodesand crystal together. As clearly seen in FIGURE 14 the cocoon 112 shownin phantom lines is of ellipsoidal configuration to accommodate the endsecured electrodes, however it is to be understood that any suitableform of cocoon can be used just as easily.

Referring to FIGURES l5 and 16 the contact strips and electrode mountingillustrated in FIGURE 13 are shown applied to a rectangular crystal 114,similar numerals indicating similar parts. In FIGURES 15 and 16 a striptype cocoon similar to that illustrated in FIGURES 9 and 18 is shownapplied to crystal 114, however in this form the depressed portion orbubble is shown as a rectangle, generally indicated 116, however, hereagain it should be noted that any desired shape or" bubble is possible.I

The shield or bubble can also be formed directly around the component bymounting the electrode suspended crystal on a suitable fixture andextruding a tubular shield in spaced relation around the component andthen sealingly crimping the tube about the electrodes for support and atthe opposite end to form a fluid tight hollow shield around thecomponent.

The evacuation procedure of the hollow bubbles or shields can beaccomplished by methods other than using hollowing heated needle 66. Apreferred method is to assemble the shield upon the circuit component ina chamber in which the atmosphere conditions may be controlled by eitherthe evacuation of the chamber or by providing an inert atmosphere.Illustrative apparatus for so assembling the units is shown in FIGURE17.

Numeral 118 generally indicates a well-known bell jar apparatus, forproviding a chamber in which the atmosphere may be controlled. Theapparatus comprises a base 1'20 and a glass bell jar 122. Stand 124 ismounted at the near center of the base and is provided at its top with amounting fitting 51 having a pair of spaced openings for receivingmounting pins 52 and 54 of a crystal, which for purposes of illustrationis similar to the crystal assembly shown in FIGURE 4. A pair of rigidfluid lines 126 and 128 are mounted in spaced relation on base are benttoward each other at their upper ends as at 130 and 132, respectively.Lines 126 and 128 extend through base 120 and are commonly connected byT-fitting 142 to line 143 which is connected through a control valve toa common source of fluid pressure (not shown). Mounting members 134 and136 are provided with integral piston portions 138 and 140,respectively, which are received with a smooth sliding fluid tight fitin the bores of portions 130 and 132, respectively. As clearly seen inFIGURES 17, mounting members are mounted so as to never contact crystal20'. For purposes of explanation mounting members 134 and 136 are shownto be of hemispherical configuration for mounting hemispherical bubbles60 and 62, however, it is to be understood that the shape of themounting members will be varied for other configurations of cocoons orshields. Tension springs 144 are secured to each mounting member at oneend and have their other ends secured to an anchor plate 146 secured tothe outer periphery of portions 130 and 132. The normal tension ofsprings 144 hold mounting members 134 and 136 in their retractedpositions, as

clearly seen in FIGURE 17. Flexible vacuum lines 148 and 150 areconnected at one end to openings 152 and 154 in mounting members 134 and136 for creating a vacuum within mounting members 134 and 136 to retainhemispherical bubbles 60 and 62 therein. Vacuum lines 148 and 150 extendthrough base 120 and are commonly connected by fitting 156 to a line 158from a common vacuum source. Vacuum lines 148 and 151? are flexible toallow for operational movement of mounting members 134 and 136.

Heating elements 160 are circumferentially mounted within each mountingmember and are disposed adjacent the face of the base of each mountingmember to provide a localized heating for a purpose to be explained.Electrical leads 162 are connected to the heating elements and extendexteriorly of the bell jar to be connected to a source of electricalcurrent.

A standard pipe fitting 164 is provided in base 120 for evacuating orproviding an inert atmosphere within the interior chamber of bell jar118 in the well-known manner.

In operation, hemispheres 60 and 62 are placed in mounting members 134and 136, respectively, and are held therein by a suction acting on thesurface of the hemispheres created by the vacuum in lines 148 and 15%. Acrystal assembly, generally designated 166, is mounted on stand .124- sothat crystal 20 is within a space defined by the peripheries of thehemispheres and the electrodes 34 and 36 are in a plane parallel to thebases of the hemispheres. The interior of bell jar 118 is then evacuatedby well-known means through fitting 164 and if desired an inertatmosphere created within the bell jar by subsequent introduction of aninert gas, such as nitrogen. Fluid pressure is then applied throughlines 126 and 128 to pistons 138 and 140. This fluid pressure forces themounting members toward each other and causes the bases of hemispheres60 and 62- which protrude slightly from the mounting members, as clearlyseen in FIGURE 17, to abut each other and also tightly compresselectrodes 34 and 36 therebetween. Current is applied to leads 162 toheat elements 166. Since the heating elements are located only .at thebases of the mounting members this heating will be locally concentratedto soften the contacting bases of plastic hemispheres. As the opposedfaces of the hemispheres are softened fluid pressure will, by moving themounting members slightly closer together, compress the plastichemispheres together to form a complete bond. It will be noted fromFIGURE 17 that the hemispheres 60 and 62 will never be forced togethertoo much and interfere with crystal 20 since the opposed faces ofmounting members 134' and 136 will abut and act as limiting means tothe. amount of compression placed on hemispheres 60 and 62. Current isthen cut oflf from leads 162 and the heating'elements are permitted tocool permitting the joined hemispheres to cool whereby a rigid fluidtight joint is formed and an evacuated or inert atmosphere is maintainedabout crystal 20. When the joined hemispheres have cooled sufiicientlyto assure a good bonded joint, fluid pressure is released from lines 126and 128 to permit springs 144 to separate mounting members 134 and 136.Atmospheric pressure is allowed to enter the bell jar and the assembledcrystal and cocoon is then removed, and the procedure repeated forsubsequent assemblies.

From the foregoing description it will be seen that I have invented anovel structure and method for protecting delicate crystalline circuitcomponents from contact with any foreign substances which might affectthe accuracy 8 of operation of such components. It will also be readilyseen that my novel structure and method permit earlier testing of suchcomponents, reduce the number of rejected units, reduc the manufacturingcosts, and assure greater accuracy and eflicient operation.

This invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changesWhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

l. The method of constructing a sealed enclosure for electrical circuitcomponent means comprising the steps of providing a pair of thin,non-collapsible sheets of relatively nonvolatile plastic material;forming a non-collapsible blister in at least one sheet in a centralposition away from the margin of the sheet; mounting said sheets in aface-to-face position together with circuit component means smaller thansaid blister positioned in the center of the interior spaced from theWalls of said blister with electric terminals on said component meansextending beyond the margin of said sheets; sealing said sheets togetheraround said blister and along a portion of the length of said electricalterminals to form a gas tight protective enclosure for said componentmeans; piercing the sealed enclosure with a heated needle; producing acontrolled atmosphere inside said sealcd enclosure; and maintaining theneedle hot while withdrawing it so that thematerial in the vicinity ofthe needle is in a plastic condition and will immediately seal theopening made by the needle as it is withdrawn.

2. The method of constructing a sealed enclosure for electrical circuitcomponent means comprising the steps of providing a thin sheet ofrelatively nonvolatile plastic material; molding spaced depressions insaid sheet; cutting said sheet between molded depressions therebyforming sections each having at least one depression surrounded byundepressed edge portions; mounting two pieces of said plastic material,at least one of which is a sheet section having a molded depression,together with circuit component means positioned in the interior of themolded depression with electrical terminals on said component meansextending beyond the edge portion of said section; sealing theundepressed edge portions of said pieces together around said depressionto form a gas tight protective enclosure for said component means;piercing the sealed enclosure with a heated needle; producing acontrolled atmosphere inside said sealed enclosure; and maintaining theneedle hot while withdrawing it so that the material in the vicinity ofthe needle is in a plastic condition and will immediately seal theopening made by the needle as it is withdrawn.

References ited in the file of this patent UNITED STATES PATENTS1,387,805 Roberts Aug. 16, 1921 1,713,755 Gibson May 21, 1929 2,266,070Pierce Dec. 16, 1941 2,486,758 Pfeiifer Nov. 1, 1949 2,615,565 Bower etal Oct. 28, 1952 2,704,880 rennan Mar. 29, 1955 2,893,182 Pies July 7,1959

